FreeBSD supports the SCSI ZIP drive out of the box, of course. The ZIP drive can only be set to run at SCSI target IDs 5 or 6, but if your SCSI host adapter's BIOS supports it you can even boot from it. I don't know which host adapters let you boot from targets other than 0 or 1... look at your docs (and let me know if it works out for you).
ATAPI (IDE) Zip drives are supported in FreeBSD 2.2.6 and later releases.
FreeBSD 3.0-STABLE contains support for the parallel Zip However, you will need to build a new kernel with support for ppbus (Parallel Port Bus) in order to use the Zip. See the LINT configuration file for examples.
Also check out this note on removable drives, and this note on 'formatting'.